Comparison of Application of Radiopharmaceutical ¹⁸F-FAPI and ¹⁸F-FDG in PET/CT Imaging for Postoperative Metastatic Lesions of Gastric Cancer and Colorectal Cancer

OBJECTIVE  To compare the application value of two different PET radiopharmaceutical: ¹⁸F-FAPI-04 and ¹⁸F-FDG, in postoperative metastatic lesions of gastric cancer and colorectal cancer.

METHODS  A prospective study enrolled 22 postoperative patients with gastric cancer and colorectal cancer(16 males and 6 females, aged 49−71 years) between May 2023 and March 2024. Each patient underwent both ¹⁸F-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT within one week. Subsequently, clinical and imaging data were analyzed. The pathological results of surgical or needle biopsy specimens from the lesions served as the gold standard for diagnosis. For patients who did not undergo histopathological examination, the diagnostic reference standard included laboratory tests, imaging findings, follow-up results, and clinical comprehensive evaluations. To compare the maximum standard uptake value(SUV_max) and target to background ratios(TBR) of ¹⁸F-FAPI-04 and ¹⁸F-FDG PET/CT imaging in postoperative metastatic lesions of gastric cancer and colorectal cancer by using the Wilcoxon signed-rank test. Additionally, the McNemar test was utilized to compare the detection rates of ¹⁸F-FAPI-04 and ¹⁸F-FDG in PET/CT imaging of postoperative metastases of gastric cancer and colorectal cancer.

RESULTS  Compared with the SUV_max of ¹⁸F-FDG in metastatic lesions, the SUV_max of ¹⁸F-FAPI-04 in peritoneal metastasis lesions6.9(4.4, 8.0) vs 1.9(1.0, 2.7), z=−5.580; P<0.001) and metastasis lymph nodes6.2(4.5, 5.3) vs 5.2(3.1, 10.7), z=−2.170, P=0.03 were significantly higher, while difference of SUV_max in liver metastatic lesions7.8(5.3, 9.0) vs 8.1(5.3, 10.8), z=−1.57, P=0.875), and bone metastatic lesions6.2(3.7, 8.2) vs 5.2(3.0, 7.9), z=−1.244, P=0.214 had no statistical difference. Compared with the TBR of metastatic foci in ¹⁸F-FDG PET/CT images, in ¹⁸F-FAPI-04 PET/CT images, the TBR of peritoneal metastatic lesions5.4(3.4, 6.4) vs 1.2(0.7, 1.7), z=−5.580, P<0.001, metastasis lymph nodes5.4(2.8, 7.2) vs 3.9(2.5, 5.2), z=−4.698, P<0.001), liver metastatic lesions6.3(2.5, 9.4) vs 3.3(2.0, 3.9), z=−2.312, P=0.021), and bone metastatic lesions7.6(3.6, 10.2) vs 4.3(2.9, 5.9), z=−2.194, P=0.028) were significantly higher. In addition, compared with ¹⁸F-FDG, ¹⁸F-FAPI-04 had a higher detection rate of peritoneal metastasis100%(41/41) vs 26.8%(11/41), P<0.001 and lymph node metastasis92.6%(50/54) vs 77.8%(42/54), P<0.021, but there was no significant difference in the detection rate of liver metastasis100%(9/9) vs 100%(9/9) and bone metastasis100%(12/12) vs 100%(12/12).

CONCLUSION  ¹⁸F-FAPI-04 has better performance than ¹⁸F-FDG in PET/CT imaging of lymph node metastasis and peritoneal metastasis in postoperative patients with gastric cancer and colorectal cancer, and ¹⁸F-FAPI-04 has advantages in the restaging of postoperative patients with gastric cancer and colorectal cancer, which is helpful for making clinical decisions.